NationalNational PestPest AlertAlert

Soybean Rust Phakopsora pachyrhizi and P. meibomiae

Distribution and Transmission Two fungal species, Phakopsora pachyrhizi and P. meibomiae, cause soybean rust and are spread primarily by windborne spores that can be transported over long distances. Asian soybean rust, P. pachyrhizi, the more aggressive of the two species, was first reported in Japan in 1903 and was confined to the Eastern Hemisphere until its presence was documented in Hawaii in 1994. Currently, dis- tribution of P. pachyrhizi includes Africa, Asia, Australia, Hawaii, and South America. P. pachyrhizi’s rapid spread and severe damage with yield losses from 10 to 80% have been reported in Argentina, Asia, Brazil, Paraguay, South Africa, and Zimbabwe. In November, 2004, the presence of P. pachyrhizi was confirmed in the continental United States. Seedborne transmission of the disease has not been documented, but there is some concern that seed lots may contain small amounts of infected plant debris capable of spreading the pathogen. To date, seed lots have not proven to be a pathway for the disease. Clouds of Soybean rust lesion types and characteristics of early symptoms of spores are released if infected plants are disturbed by wind or by in- soybean rust and bacterial pustule. dividuals walking through rust-infected areas. Individuals who are sampling for soybean rust may transport spores from one area to another on clothing. If clothing is exposed to spores, care should be Host Range taken to prevent the spread of soybean rust to uninfected locations. P. pachyrhizi is capable of infecting more than 90 species of legumes; however, the number of legumes infected in nature is un- known. Kudzu is widespread in the United States and could serve as a reservoir for the soybean rust pathogen. The broad host range of this fungal pathogen increases the likelihood of rapid spread once introduced into the United States.

Symptoms and Disease Development Soybean rust symptoms are similar for P. pachyrhizi and P. meibomiae species. Symptoms begin on the lower leaves of the plant as small lesions that increase in size and change from gray to tan or reddish brown on the undersides of the leaves. Lesions are most common on leaves but may occur on petioles, stems, and pods. Soybean rust produces two types of lesions, tan and reddish Symptoms in non-tolerant (left) and tolerant (right) soybean brown. Tan lesions, when infected with soybean rust. mature, consist of small pustules (uredinia) surrounded by slightly discolored necrotic Sample Submission area with masses of tan spores (urediniospores) on the lower leaf surface. Reddish brown lesions have a larger reddish brown necrotic Submit samples to your state’s university diagnostic laboratory or area, with a limited number of pustules (uredinia) and few visible Department of Agriculture diagnostic laboratory for identification spores (urediniospores) on the lower leaf surface. Once pod set (contact university extension personnel for the address of the begins on soybean, infection can spread rapidly to the middle and diagnostic laboratory). Each state is developing an invasive species upper leaves of the plant. response program as part of the USDA National Plant Diagnostic Network. If samples are identified as soybean rust by state Environmental conditions impact the incidence and severity of diagnosticians, species verification by molecular analysis will be soybean rust. Prolonged leaf wetness combined with temperatures required. between 59 and 86ºF and humidity of 75–80% is required for spore germination and infection. Under these conditions, pustules form within 5–10 days and spores are produced within 10–21 days. High Management Recommendations levels of infection in soybean fields result in a distinct yellowing and All commercial varieties currently available are highly susceptible. browning of fields and commonly, premature senescence in plants. Current research includes screening germplasm for resistance and evaluating fungicide efficacy. Early detection is required for the Identification of Soybean Rust most effective management of soybean rust. Monitoring soybean fields and adjacent areas is recommended throughout the growing Molecular analysis provides rapid and accurate identification season. Fungicide applications may reduce yield loss, depending on to differentiate between P. pachyrhizi and P. meibomiae. Early the plant developmental stage, time when soybean rust is detected, symptoms of soybean rust resemble bacterial pustule (Xanthomonas and fungicide application method. For efficacy information on axonopodis pv. glycines) and brown spot (Septoria glycines). Soybean fungicides labeled for use on soybean, consult university extension personnel in your state.

For more information on soybean rust, visit our Web site at http://www.ncipm.org/soybeanrust This publication was produced and distributed by USDA-CSREES Integrated Pest Management Centers in cooperation with the National Plant Diagnostic Network, APHIS, ARS, and the 1862 Land-Grant Universities. For more information regarding the development of this document, contact Susan T. Ratcliffe at [email protected] or by phone at (217) 333-9656. Photos courtesy of Glen Hartman (USDA-ARS) and David Riecks (University of Illinois, College of Agricultural, Consumer and Environmental Sciences); scanning electron microscopy of spores courtesy Various stages of soybean rust on soybean leaves. of Morris Bonde (USDA-ARS); and soybean rust illustration courtesy of Joel Floyd (USDA-APHIS-PPQ). Editor: Julie L. Todd (Department of Entomology, Iowa State University). Graphic designer: Gretchen Wieshuber rust can be distinguished from bacterial pustule and brown spot (Studio 2D, Champaign, IL). by examining the lesions under a hand lens (20×) or dissecting microscope. The mature soybean rust lesion contains cone-shaped 1862 Land-Grant Universities pustules with a pore on the top with spores inside or on top of the cone. Auburn University University of Alaska University of Arizona University of Arkansas University of California Colorado State University University of Connecticut University of Delaware University of the District of Columbia Sample Collection Procedures University of Florida University of Georgia University of Guam University Collect samples immediately if you suspect soybean rust is present of Hawaii University of Idaho University of Illinois Purdue University Iowa State University Kansas State University University of Kentucky Louisanna on soybean or other hosts. Place each plant sample in a self-locking State University University of Maine University of Maryland University plastic bag and maintain under cool conditions (refrigeration). of Massachusetts Michigan State University University of Minnesota Mis- Place samples in sealed paper bags if cool conditions are not sissippi State University University of Missouri Montana State University available. Once refrigeration is available, each sealed paper bag University of Nebraska University of Nevada University of New Hampshire should be placed inside a self-locking plastic bag before cooling. Rutgers New Mexico State University Cornell University North Carolina Leaves should be kept flat by placing them between paper towels State University North Dakota State University Ohio State University or pieces of paper. Record the following information for each Oklahoma State University Oregon State University Pennsylvania State sample collected: date; host plant; collector’s name; phone number; University University of Puerto Rico University of Rhode Island Clemson collection location within field; and location of field, including University South Dakota State University University of Tennessee Texas state, county, township, and nearest road intersection. Global A&M University Utah State University University of Vermont University positioning system location information is requested if available. of the Virgin Islands Virginia Polytechnic Institute & State University Washington State University West Virginia University West Virginia State Mark sample containers with a permanent marker and print all University University of Wisconsin University of Wyoming information.